CO indicators

[5422]

Many years ago when I was a kid I got gassed bad by CO and was sick for a while after. It sucked. Anyway after that experience I was hyper vigilant about being exposed to it again. For years all I used and relied (and religiously replaced) on was those stick on eye and spot indicators and figured they are pretty accurate. Even boasting that our 140 was CO free and clear.

A friend of mine has a expensive sensitive CO indicator and lent it to me for a few days. Pretty eye opening as far as what the levels were in different regimes of flight and ground ops. Granted these were pretty low values but they were higher than I expected. Makes me want to pressure test the exhaust system and seal some door gaps. I was kinda shocked to see an OHSA acceptable exposure level of 50 ppm for 8 hours.

I’ve seen those spot indicators change color and know they work. But from the looks of it they have to be exposed for a while to turn unless it’s a really high amount CO. Makes sense though if you are behind an internal combustion engine in different situations that make the CO level highly variable. The 3 unexpired spot indicators never registered anything during the below flight (done with cabin heat on and off).

Taxi/run up. 3-13 parts per million (PPM)
Takeoff roll. 0 ppm
Shallow climb. 0-7ppm
Steep climb. 13-27 ppm
Cruise (vents closed). 8 ppm
(vents open). 0 ppm
Steep descent. 23-35 ppm
Slip to landing (left rudder) 42-54 ppm
Taxiing with 12 kt tailwind for approx 5 mins. 57-61 ppm

Wonder what the CO levels on a dead calm day in heavy stop and go street traffic are going to be. Anyway my question is do any of you have digital CO indicators installed in your 140 and if so what kind?

[klyde sessna]

Which type of exhaust system do you have. Original strait pipes or Cessna 150 style? Shrouds, pancake or round mufflers?

[5422]

C-150 setup with almost 100 hours since new. Tight with no grey exhaust stains in usual leakage areas (manifold to cylinder/muffler to tailpipe connection). Pressure checked fine at annual. Thinking the pilot side door gap might need some better sealing.

[tonycondon]

I have a digital CO meter. it reads steady at 3-5 ppm from start of flight to finish with the heat on.

Aero Fabricators exhaust is 4 years old.

[V529]

I had a hand held electric unit(battery powered) at my last shop. We used it from time to time on whatever needed it. It would read right down to 2ppm. I flew with it in various airplanes (including mine) and it never registered anything(above the standard 2ppm, which I always presumed was "zero" for all intents and purposes).

I've also used it in homes to make sure the furnace didn't have a cracked heat exchanger. I know it works and works well. Once you get within about 5 feet of the tail pipe of my truck, even outdoors, it goes bonkers.

[a64pilot]

As part of the Certification test flights of a new aircraft, I was required to monitor and record the cockpit CO level, to do this we used a Scott mini-sa CO detector, it would detect down to 1PPM and had to be sent off for calibration every 90 days. Real slick instrument, flashing LED, vibration and the display would latch at highest level recorded, small and light, I wore it on my shoulder harness
I’ve flown the 140 with it, and have recoded 0 PPM of CO, this is a stock 46 exhaust.
There are several consumer grade electronic CO detectors available, but all electronic CO detectors have a life span and have to be replaced every so often.
Don’t use a house CO detector, their threshold of alarm is quite high

You shouldn’t be getting any CO in flight, on the ground depending on wind you may with any aircraft.
I’d look for openings in the firewall, missing screws etc.

[5422]

Bought a sensitive digital detector (from sportys) that is pretty close to the sensitivity of the expensive one I borrowed (Fluke) to chase down where the leak/problem areas are. Figured with those 3 CO detectors ( one on each doorpost and one on panel) they would have changed color even on 3 hour flight. Anyway I’m panel mounting a digital indicator on both our planes. Winter flying with the heat on all the time demands it. It was funny today we took the digital indicator out on a flight in our PA-18 and I figured it woulda had some indications being how drafty a Cub is anyway. Some mods like belly pods and such direct exhaust tainted airflow to windows and door gaps.

In flight zilch nada nothing the only time it got elevated was at the hold short line parked next to three planes even then it was only 9ppm. Funny how a few local pilots say I’m overreacting about a “little” CO that doesn't trip the tried and true spot indicators. But then again none of them have been in the hospital with bad CO poisoning.

FDC7D12E-3739-4E4C-95FD-18A9E49D7F8F.jpeg (138.35 KiB) Viewed 2943 times

[a64pilot]

your not overreacting.
The thing about CO poisoning is it’s cumulative, it doesn’t clear right away when you get into clean air like you would think it does, it stays bonded to Hemoglobin, so multiple exposures add up.

I don’t know how long it takes to clear from the blood stream though.

According to this it takes four to six hours for half of the CO to clear the bloodstream, first hit on Google.

https://www.drugs.com/health-guide/carb ... oning.html

However if I understand it correctly the hemoglobin has an affinity for it, so while it may take a very long time to clear, your blood will absorb it very quickly.

Now this is going back to flight school for me, so my memory isn’t good, but if memory serves even a small amount of CO has other effects more important to aviation, it’s effects worsen in high altitude, and I believe even a small amount has a large effect on night vision, and I think it effects motor skills even in low doses?

[6344]

Were you able to track down where the CO leak was coming from? I just installed a new C-150 exhaust system and I am still registering some CO on my digital detector. It seems to be the worst during climb out and approach to land. At Cruise the levels are low to none. I've looked for leak points in the firewall but nothing is sticking out. Just curious if you found something that I am overlooking.

[2356]

Two leak points come to mind. The hole where the fuel line exits the firewall. Where the firewall attaches to the fuselage is not air tight. How else would oil migrate on the floor below the rudder pedals.